Subject: + exitc-call-proc_exit_connector-after-exit_state-is-set.patch added to -mm tree To: guillaume@xxxxxxxxxxx,davem@xxxxxxxxxxxxx,matt.helsley@xxxxxxxxx,oleg@xxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Mon, 24 Feb 2014 13:53:29 -0800 The patch titled Subject: kernel/exit.c: call proc_exit_connector() after exit_state is set has been added to the -mm tree. Its filename is exitc-call-proc_exit_connector-after-exit_state-is-set.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/exitc-call-proc_exit_connector-after-exit_state-is-set.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/exitc-call-proc_exit_connector-after-exit_state-is-set.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Guillaume Morin <guillaume@xxxxxxxxxxx> Subject: kernel/exit.c: call proc_exit_connector() after exit_state is set The process events connector delivers a notification when a process exits. This is really convenient for a process that spawns and wants to monitor its children through an epoll-able() interface. Unfortunately, there is a small window between when the event is delivered and the child become wait()-able. This is creates a race if the parent wants to make sure that it knows about the exit, e.g pid_t pid = fork(); if (pid > 0) { register_interest_for_pid(pid); if (waitpid(pid, NULL, WNOHANG) > 0) { /* We might have raced with exit() */ } return; } /* Child */ execve(...) register_interest_for_pid() would be telling the the connector socket reader to pay attention to events related to pid. Though this is not a bug, I think it would make the connector a bit more usable if this race was closed by simply moving the call to proc_exit_connector() from just before exit_notify() to right after. Signed-off-by: Guillaume Morin <guillaume@xxxxxxxxxxx> Cc: Matt Helsley <matt.helsley@xxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/exit.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN kernel/exit.c~exitc-call-proc_exit_connector-after-exit_state-is-set kernel/exit.c --- a/kernel/exit.c~exitc-call-proc_exit_connector-after-exit_state-is-set +++ a/kernel/exit.c @@ -804,7 +804,6 @@ void do_exit(long code) module_put(task_thread_info(tsk)->exec_domain->module); - proc_exit_connector(tsk); /* * FIXME: do that only when needed, using sched_exit tracepoint @@ -812,6 +811,7 @@ void do_exit(long code) flush_ptrace_hw_breakpoint(tsk); exit_notify(tsk, group_dead); + proc_exit_connector(tsk); #ifdef CONFIG_NUMA task_lock(tsk); mpol_put(tsk->mempolicy); _ Patches currently in -mm which might be from guillaume@xxxxxxxxxxx are exitc-call-proc_exit_connector-after-exit_state-is-set.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html